Fibre Channel 8B/10B Encoding - How IT Works For The IBM Code - Encoding Tables

Encoding Tables

Note that in the following tables, for each input byte, A is the least significant bit, and H the most significant. The output gains two extra bits, i and j. The bits are sent low to high: a, b, c, d, e, i, f, g, h, and j; i.e., the 5b/6b code followed by the 3b/4b code. This ensures the uniqueness of the special bit sequence in the comma codes.

The residual effect on the stream to the number of zero and one bits transmitted is maintained as the running disparity (RD) and the effect of slew is balanced by the choice of encoding for following symbols.

The 5b/6b code is a paired disparity code, and so is the 3b/4b code. Each 6- or 4-bit code word has either equal numbers of 0s and 1s (a disparity of 0), or comes in a pair of forms, one with two more 1s than 0s (four 1s and two 0s, or three 1s and one 0, respectively) and one with two less. When a 6- or 4-bit code is used that has a non-zero disparity (count of 1s minus count of 0s; i.e., −2 or +2), the choice of positive or negative disparity encodings must be the one that toggles the running disparity. I.e., the non zero disparity codes alternate.